Automatic telephone selector



w 0, 1935- B. .1. BRANDER AUTOMATIC TELEPHONE SELECTOR Filed NOV. 16, 1934 I 6 Sheets-Sheet l 10, 1935. B. J. BRANDER I AUTOMATIC TELEPHONE SELECTOR 6 Sheets-Sheet 2 7 Filed Nov. 16, 1934 Dec. 10, 1935. J A E 2,024,089

AUTOMATIC TELEPHONE SELECTOR Filed Nov. 16, 1934 6 Sheets-Sheet 3 10, 19350 B. J. BRANDER 4, AUTOMATIC TELEPHONE SELECTOR Filed Nov. 16, 1934 6 Sheets-Sheet 4- v Dec" 10, 1935. B. J. BRANDER AUTOMATIC TELEPHONE SELECTOR Filed Nov. 16, 1954 6 Sheets-Sheet 6 I] IEIII'I] If Patented Dec. 10, 1935 UNITED STATES PATENT OFFICE Application November 16, 1934, Serial No. 753,376 In Sweden October 5, 1932 23 Claims. (Cl. 179-2753) This invention refers to automatic telephone selectors, driven by individual electric motors, and comprises partly an improved motorl or driving device in combination with selectors of various kinds, and partly an improved selector of the so-called multiple brush or panel type, which is s ecially suitable for driving by means of the improved motor.

The invention also includes a particular construction of the multiple contact bank for the selectors.

The main object of the invention is to provide the selector with a most efficient miniature electric motor, designed in accordance with standardlzed principles of ordinary alternating current synchronic motors, said motor being suitable for driving the selector forwards and backwards, either by means of continuous current impulses in synchronism with the subscribers dial or similar impulse sender-or by means of ordinary alternating current-during non-numerical movements of the selector.

A further object of the invention is to produce a selector of the simplest possible mechanical design, by the combination with the improved driving device.

With regard to driving devices, at present used for telephone selectors, it is well known that the step-by-step drive is still retained in all systems using selectors of the Strowger type. The that this driving method is not an ideal one, has been realized by telephone engineers long ago. The drawbacks of the step-by-step system are obvi0us-the vibration, noise and excessive wear caused by the parts constantly moving to and fro, are the most prominent disadvantages. A further undesirable feature is the necessity using very strong current impulses for the driving magnets.

To avoid the drawbacks of the stey-by-step e, power driven systems have been designed, c 1g permanently rotating shafts, driven by ordinary electric motors, and electro-magnetic clutches for transmitting the rotary motion to the switch arms while being set. Such systems, however, a such more expensive than the step-bystep system, on account of the great number of r: ating shaits and gear wheels and also because systems require registers or similar impulse storing devices.

In order to obviate the drawbacks of both the above-mentioned driving methods, it has been s estcd to use individual motors-simi1ar to cra electromotors, but of course very small and lightfor driving the selectors. A

driving device of this kind is shown in the British Patent No. 252,932, which describes a selector driven by a small three-phase motor. The threephase system, according to said patent, however, requires rather complicated circuits and re- 5 lay combinations. With modifications of the driving system according to the present invention, alternating current motors of the singlephase, two-phase or three-phase type may be utilized. Driving devices with a non-polarized, 10 rotatable armature have also been suggested for driving selectors. A motor of this kind is not suitable for driving in both'directions without complicated circuits or commutating devices. Further it is obvious, that a motor with a non- 15 polarized armature cannot have the same efficiency as a motor with a polarized armature working in a perf ctly balanced magnetic field as in the case of ordinary synchronic motors for power distribution.

The new driving device for the selectors is designed to satisfy the following requirements.

1. The selector shall be driven by a most efficient alternating current motor without commutator or interrupting contacts, the rotation of 25 the armature taking place in either desired direction and being easily reversible.

2. In case of numerical working of the selector the motor armature shall rotate in either desired direction by means of direct current impulses 30 from a relay, or a set of relays, thereby moving the selector in synchronism with the impulse sender.

In case of non-numerical Working of the selector a should, for sake of highest efficiency be 35 possible to drive the motor by alternating current.

To attain the said object, the selector may be provided with a two phase alternating current synchronic motor, the rotating field of which, 40 in case of numerical working, is produced by means of impulses from a relay, or a set of relays, Working in synchronism with a calling subscribers dial or a similar impulse sender, said relay impulses having collectively the character of two 45 alternating currents with a phase difference of approximately 90, while, in case of non-numerical working the field coils of the motor receive normal two phase alternating currents or a combination of continuous current impulses hav- 50 ing collectively the character of two alternating currents with a phase difference of approximately 90.

In the accompanying drawings, Fig. 1 is a front view of a selector of the panel type including the feature of the present invention. Fig. 2 is a plan view of the same selector mounted on the selector rack together with a second selector mounted on the opposite side of the rack. Fig. 3 is a cross section along the line IIII[I in Fig. 2. Fig. 4 is a diagram of connections which may be applied to a selector of the kind shown in Figs. 1-3. Figs. 5 and 6 are two modified diagrams of connections and relay arrangements. Fig. '7 is a front view of a contact bank for 50 lines with room for 6 line finders and 6 connectors. Fig. 8 is a lateral view, partly in section, of said contact bank. Fig. 9 is a horizontal section through the bank according to line IX-IX in Fig. 7. Figs. 10 and 11 show details of Figs. '7 and 9. Fig. 12 is a vertical section through the bank along the line XIIX[I in Fig. 10. Figs. 13-17 show details pertaining to the contact bank.

Referring at first to Figs. 1-3, in order to reduce the load of the driving motor, thereby making it possible to use a motor of very small size, the brush carrier is arranged horizontally in front of a multiple contact bank of the fiat type. The selector proper is provided with only five brushes, thus its capacity is only 50 lines, but it will be easily understood, that a selector for the normal capacity of 100 lines will differ only with regard to the number of brushes and the size of the multiple bank.

This selector is mainly composed of two movable switching members, namely a slide Y which is mounted on rollers on the base plate .9 of the selector and carries the multiple brushes 0, and a rod Z mounted on rollers in a similar manner on top of the slide Y and having fixed to it at one end a toothed rack z engaging with the gear of the motor M in such a manner that it can be moved a short distance forwards and backwards by means of the motor.

The brushes C are mounted on pivots d in such a manner that they do not in their normal position touch the contacts e of the multiple bank, but may be swung out successively against the contact bank by means of a corresponding number of studs 1 on the rod Z engaging with projections or lugs g on the brush holders.

The brushes C have their contact springs a, b, c electrically connected with the respective springs a, b, c of the neighbouring brushes by means of helical springs T, which at the same time serve for holding the brushes in their normal position when they are not influenced by the studs 1 on the rod Z. a

As already mentioned, the multiple contact bank is of the panel type, made up of metal strips with projecting lugs which form the actual multiple contacts.

The rod 2 carries a pawl 70 which is movably mounted on a pivot t in such a manner that it can swing out to the one or the other side, but it is held in its middle position by means of a flat spring it. This pawl 7c has a downward projecting arm or pin 12 which engages with the teeth of a ratchet Z fixed on the slide Y. A spiral spring at has one end inserted in the fixed end of the fiat spring 11. while the other end is inserted in a small bracket fixed on the slide Y. Another spiral spring It may be arranged between the slide Y and the base plate s in order to hold the slide more firmly in its normal position against a stop pin 11 while the rod Z is returning to normal. It however not necessary to use both springs a: and h but one of them may be left out. Further there is arranged, on the slide Y a pair of contact springs, the contact n of which is held open by means of an insulating pine when the rod Z and the slide Y are in normal position in relation to each other. On the base plate .5 there is another pair of contact springs, the contact 10 of which is closed by an insulating pin q 5 on the rod Z when the latter is moved to its extreme left position. This contact 17 serves, by means of a relay, to reverse the motor and the movement of the rod Z in order to restore the latter to its normal position. 10

In consequence of the rod Z and the slide Y being arranged horizontally and made of a thin and rigid material, it is possible to impart to them a step-by-step motion in synchronism with the impulses sent from the subscribers dial by means 15 of the rotating motor armature which is also very small and light. With regard to the driving ac tion of the motor, it should be noticed that the motor armature, as will be further explained below, for every impulse from the dial, receives 9 four impulses from the relays. This obviously effects a uniform movement of the motor armature and further has the advantage, that the amount of work to be carried out by each of these four impulses naturallywill be only about one fourth 25 of the work necessary for driving the switching member one full step forward, which means that the strength of current or, properly speaking, the amount of energy spent on each of the four secondary impulses need not be more than approxi- 30 mately one fourth of the amount of energyrequired if only one impulse should drivethe switchingmember a full step. The advantage of this is, that the relay contacts, by which the impulses are sent to the motor, are much less liable to spark and wear out than the impulse contacts in an ordinary step-by-step system.

The motor M is, as mentioned above, a small two-phase synchronic motor, having two pairs of field coils, arranged in an angle of 90 in relation to each other. The two-pole armature 3 carries a single coil through which a continuous current is sent while the motor is working. The shaft of the armature 3 carries a small pinion engaging with a toothed wheel 5 the shaft of which also carries a pinion which engages with the toothed rack e at the end of the rod Z. The size of the gear wheel 5 and the said pinions are proportioned in such a manner that a full revolution of the motor armature 3 causes the rod Z to move a distance 5 equal to the division of the sets of line contacts in the multiple field.

According to the diagram of circuits Fig. 4, a, common battery B supplies the current to the motors M of all the selectors as well as the relays 'for the control of their movements. In order that the number of relay contacts for sending the current impulses through the field coils of the motor may be reduced as far as possible, the middle point of the battery B is earthed as well as the return conductor of the motor.

The operation of the selector When the subscriber on lifting his receiver, in' some well known manner, for instance by means 5 of a line finder, has obtained connection with the final selector, shown in the diagram Fig. 4, current flows to the line through the windings of a relay RI, which closes a local circuit for a sluggish relay R3, the latter relay then sending current by its contact 35 from the plus pole of the battery through the windings 4 of the motor armature and by the contacts 6 and 7 through the field coils I and 2 to earth. The motor armature is thereby set to the position shown in the diagram,

in case it did not, in its idle state, already occupy this position.

When the subscriber then turns his dial, thereby sending the tens impulses to the relay RI, a series of interruptions of the line current is effected in the usual way and the relay RI releases its armature once for every break of current. In the meantime the relay R3 retains its armature. When the relay RI releases its armature the first time, a circuit including a slow action relay R1 is closed by a contact II and another circuit including an auxiliary relay R2 is closed by a contact I0. At the same time the current in the field coils 2 of the motor is reversed by the opening of the contact 6 and closing of the contact 8, which causes the motor armature to move 90 (with the sun). After a short interval the relay R2 attracts its armature, thus opening contact 1 and closing the contact 9, which effects a reverse of the current in the field coils I and a further movement of the motor-armature 90 in the same direction. When the relay RI then attracts its armature, the current in the field coils 2 is again reversed and the motor armature makes a further movement of 90. At the same time RI opens the circuit of R2, the latter relay releases, the current in the field coils is once more reversed and the motor armature completes its revolution by moving again 90. At the next opening of the line circuit in the subscribers dial the same changes of the currents in the field coils take place and the motor armature makes another revolution. Thus the motor armature will make just as many revolutions as the number of interruptions of the line current, which causes the rod Z to move just as many steps to the left and to set one of the brushes in working position.

As above mentioned, the relay R1 was excited at the first impulse by the closing of the contact II and said relay, being a sluggish one, retains its armature, in the Well known manner, during the following impulses and releases it shortly after the cessation of the whole train of impulses.

At the first turn of the motor armature the rod Z is moved one step to the left and the contact n at the same time closes a local circuit through the winding of a relay R4. This relay then remains excited until the selector returns to normal. One of its functions is to close a contact I as a preparation for the excitation of a relay R5, the object of which is to reverse the movement of the motor during the following last train of impulses. When the relay R1, at the end of the tens impulses, releases its armature, the relay R5 is excited and by changing the leads of the motor coils I and 2 prepares the reversed motion of the motor. Meanwhile the position ofthe armature is not altered because the direction of current in the coils I and 2 is the same before and after the relay R5 is excited.

When the last train of impulses actuates the relay RI, the motor coils I, 2 will receive impulses from this relay and the relay R2. as before, the only diiference being that the motor armature now revolves in the opposite direction, thus moving the rod Z to the right. The pawl k, engaging with the ratchet I now couples the rod Z with the slide Y which is also moved to the right with all the brushes C, but only the brush, set in working position will touch the multiple contacts during this movement. During this as well as the foregoing train of impulses received by the relay RI, the relay R1 is excited, opening the above mentioned circuit of the relay R5, but the latter relay keeps its armature attracted over a holding circuit closed by its own contact I5.

When the selector has been set to the desired line, a test relay R8 is connected to the last spring of the brush by means of a contact IS on the relay R1. Said relay R8 will then test the line in the Well known manner and, in case of the line being disengaged, it will pull up its armature and start the automatic call of the Wanted subscriber. The arrangements for ringing and busy signal are not shown in the drawings, as they are well known and independent of the invention.

The selector, having been set on the required line, should preferably be held in this position by some locking arrangement. The simplest way of effecting such locking, in the type of selector in question, is to send a continuous current through the motor armature and the field coils during the conversation. This method of looking is used according to the diagram, Fig. 4. The relays R, R3, R4 and R8 being excited during the conversation, current will flow from the plus pole of the battery by the relay contacts 35, 3, 24, and 25 through the motor windings 2 and a resistance H to earth. At the same time current flows through the motor windings I by the contacts 35, I and 36 while a current also passes the armature winding 4, which is connected in parallel to the field coils I and 2. This current will hold the motor armature in a fixed position, thus locking the selector during the conversation. With regard to this method of locking the selector during the conversation, the objection may of course be raised, that it involves an increase of the current consumption. To avoid this, the resistance Il, instead of being directly connected to ground, may be grounded by means of a contact 26, which acts like a burglar alarm contact, connecting the resistance IT to ground, only when it is released by opening the case or cabinet, in which the selectors are enclosed. This modified arrangement is indicated with dotted lines in the diagram Fig. 4 and is also shown in two modified diagrams, Figs. 5 and 6, which are described below. Thus it will be understood that the contact 26 is normally held open by a closed door or cover of the enclosure for the selectors. In this case, however, the spiral spring h (Fig, 2) is omitted and only the spring at is used. The selectors are then held in their speaking positions only by the friction between the active brush and the multiple contacts and this is quite sufficient so long as no person can touch the selectors. But if occasionally the door of the selector cabinet is opened, for instance by the person supervising the plant, the contact 26 will close the holding current to all selectors which are in the speaking position, thus preventing him from inadvertently moving any selector in use.

The restoring of the selectors at the end of the conversation, according to the diagram Fig.

4, depends only on the replacing of the receiver of the calling subscriber. The relay RI is then deenergized and shortly afterwards also R3. A current is closed by contact IQ of RI and 2I of R4 through the winding of R2, which closes its contact 25. When R3 has released its armature, a current is closed by its contact I9 through a winding 22 of relay Rl, causing this relay to reattract its armature and open the circuit of R2. When relay R2 then releasesfit breaks the control oi subscribers dial.

current in the relay winding 22 of RI, causing this relay to release, and this interaction between the relays RI and R2 continues until the relay R4 releases its armature, i. e. until the selector is restored to its normal position. During the said interaction of the relays RI and R2 they are sending impulses to the motor in very much the same manner as during the first train of impulses sent to the motor under the The relay R not being excited at the beginning of the restoring movement, the motor will drive the rod Z to the left, the slide Y, owing to the action of the spring a: following this movement until it steps against the stud 1'. But the rod Z will continue its movement to the left, until the pin 2) of the pawl It has passed the last tooth of the ratchet Z. In this moment the stud c closes the contact p thereby sending a current through the relay R5, causing the movement of the motor armature and the rod 2 to be reversed. The relay R5 remains excited by its own holding contact 23, while the pawl k with its pin '0 slides along the outer edge of the ratchet Z, until it arrives to its normal position at the right end of the ratchet. During the return movement of the rod Z the spring x (or it) keeps the slide Y against its stop i. When the rod Z reaches its normal position, the contact 12 is opened and the relay releases its armature, thus cutting off the current to the motor and all the relays.

The above described motor selector and the relay circuits for controlling its movements may be modified or improved in various ways without departing from the main features of the invention. The following examples of modifications may be mentioned:

(1) According to the diagram Fig. 4, the phase difference of two consecutive relay impulses to the motor is effected by means of the auxiliary impulse relay R2. This arrangement has the disadvantage that not less than five impulse contacts--5, ii, "i, 9, and IIlare required for driving the motor. This is, of course, a complication in comparison with the ordinary step-by-step system, and besides that, it is a little troublesome to adjust these impulse contacts so as to attain the proper retarding effect of the auxiliary relay R2. This relay arrangement may be modified as shown in Fig. 5.

With regard to the movements of the selector, these are, according to the diagram Fig. 5, exactly the same as according to Fig. 4 and for this reason only the modified motor circuits are described below.

The relays RI, R3, R4, R5, R6, R1, and R8, Fig. 5, correspond to the relays marked in the same way in Fig. 4. Thus the auxiliary relay R2 in Fig. 4 is, according to the modified diagram, Fig. 5, done away with.

As shown in Fig. 5 both motor circuits I and 2 are, when the relays RI and R3 have been energized, connectedon one side-to the plus pole of the battery B by the contacts 5, 6, 24, 25, and 56 andon the other sideto earth (or the middle poin of the battery) by the contact I 8 of the relay Rd. In one of the motor circuits there is inserted an inductance coil 46 and in the other circuit a non-inductive resistance 4|. The ohmic resistances of 49 and M are equal, in order that the continuous current shall be of the same value in both circuits, when the motor is being stopped. When the relay R? is pulsating in synchronism with the subscribers dial, the alternate closing of its contacts 6 and 8 produces direct current impulses of opposite directions in the motor circuits I, 2, but the impulses in one of the circuits'are retarded by means of the inductance coil 46. The iron core of this coil 40 is dimensioned to give a self induction which causes a phase difference of 5 approximately 90 or one fourth of the whole period of impulses caused by the release and the reattraction of the armature of the relay RI at a short interruption of the line current. The setting of the selector takes place in the same way as 10 described in connection with Fig. 4. With regard to the restoring of the selector, this is effected, according to Fig. 4, by the cooperation of the two relays RI and R2. As the relay R2, however, is omitted in the modified diagram Fig. 5, the restoring, in this case, is accomplished by means of an ordinary single phase alternating current genorator. As above described with reference to Fig. 4, during the period of restoration the relay R3 has released while the relay R4 has attracted its armature. This being the same case with regard to the diagram Fig. 5, the alternating current from the generator G is closed by the relay contacts 42, i3 and passes through the motor circuits 9 and 2 in parallel, the inductance coil 38 causing a retardation of about 90 in one of these circuits. Thus the motor Will, in this case, receive practically normal two phase alternating current. When the slide Y has reached its normal position, the relay R5 is excited by the closing of the contact p and R5 shifts the leads to the motor, thus reversing the rotation of its armature, causing the return of the rod Z to normal and the opening of the contact n, which cuts off the current to all the relays.

If it is preferred to use relay impulses for the restoring, this may easily be effected by arranging a local circuit with a self-interrupting contact on the relay RI, so that this relay will automatically sen-d similar impulses to the motor for the restoring as for the setting of the selector.

Thus it is evident, that the introduction of the retardation coil to a considerable extent simplifies the circuits and relays for driving the motor.

The retardation in one of the motor circuits may of course be produced by means of other well known devices for the purpose, for instance condensers. A con-denser 44 may also be used in addition to the inductance coil ie, in which case it is connected as a shunt to the corresponding motor circuit, as indicated with dotted lines in Fig. 5.

(2) The modification of the motor circuits shown in Fig. 6 comprises the arrangement of double windings on the field magnets, forming two circuits ll, 48, respectively 45!, 55, acting in opposite directions.

When the motor MI is driven by means of impulses from the relay R!, the said circuits 41, 48, respectively 4Q, 58, are alternately brought in connection with only one of the polesthe minus pole-of the central battery BI, the plus pole of which by means of a common return wire is connected with the other side of all the motor circuits ll, 48, G9, 555. As will be easily seen from the diagram, the change of polarity of the stator poles of the motor MI will thus be effected without dividing the battery in two portions or using a conductor from its middle point, as described in relation to Fig. 5. Referring to Fig. 6, the retarding of the impulses in one of the stator circuits could of course be done by means of an auxiliary relay, as in Fig. l, but in order to gain the same advantages with regard to the arrange- 75 ments of the relays as in Fig. 5, an inductance coil D may be used for said purpose.

Said inductance coil D is provided with two windings :5, 56 acting in opposite directions and connected in series with each one of the stator circuits 58 of one pair of poles. In series with the stator circuits s9, 58 of the other pair of poles are inserted two non-inductive resistanccs 52. The ohmic resistances of the two windings 25, 56 of the inductance coil D are equal and are also of the same value as the resistances 5|, 52, in order that both pairs of poles of the stator shall be equally magnetized when direct current is passing through them.

The operation of the motor Ml, Fig. 6, is, in its principal features, the same as that of the motor M, Fig. 5. The inductance coil D, however, acts partly as a retardation coil and partly as a transformer, thereby producing a greater retarding effect on the impulses in one of the stator circuits. The windings 45, 45 acting in opposite directions, the magnetic field of the coil D will be reversed every time the relay RI releases or attracts its armature. The induction effects thereby produced in the windings 45, 46 cooperate in retarding the magnetization of one pair of the stator poles by the battery current in the field coils il 5 3, when the relay R! is pulsating. The induced tension in the field circuit which is opened produces a short fiow of current, or a so-called kick, which takes its way through the resistance M, respectively 52 and the field windings 49, respectively 50. From the diagram it will easily be understood that this kick in one of the field circuits ll or 48) will flow in the same direction as the battery current just broken, but in the other circuit (49 or 50) it will flow in the opposite direction. In consequence the reversing of one pair of poles of the motor will be retarded, but in the other pair of poles accelerated. At the same time the inductance in the field circuit which is being closed by the relay RI will retard the battery current in the counteracting field circuit 48, respectively 41. It will easily be understood that these two effects of the inductance coil D will cooperate to the desired phase difference in the stator circuits.

If it is desired to use an inductance coil of smaller dimensions than a coil which, without the aid of other means, is required for producing a sufficient retarding effect, two condensers 55 may be inserted as shunts, one to each of the field coils 41, 48, as indicated with dotted lines in Fig. 6. In place of condensers, noninductive resistances preferably in the form of small glow lamps with a very fine metal filament, or the well known resistances having a fine iron wire surrounded by hydrogene, may be used for the purpose. Resistances with a high temperature coefficient like these, give a greater retarding effect, because they require a longer time for increasing their resistance to maximum than the time required for a condenser (of ordinary size) to be charged.

The above mentioned arrangement for reducing the consumption of current for locking the selector in the speaking position is more clearly shown in Figs. 5 and 6. The enclosure for the selectors has a door 53, which in the closed position keeps the contact 26 open. When the door 53 is opened by the inspector, all selectors which are in the speaking position, will receive locking current through the motor windings by the closing of the contact 26.

It is obvious that the mechanical design of the or reversed within the scope of the present invention.

With regard to the multiple contact bank for the selector of the kind referred to or of similar type, its general design has been mentioned in connection with the foregoing description of the selector and is partly shown in Figs. 2 and 3. Figs 7-17 show the multiple bank and some of its component parts separately.

In Figs. 7, 8 and 10-12 the middle portion of the multiple bank is omitted, contact groups for only two line finders-one on each side of the bank-and for two connectorsone on each sidebeing visible.

Referring to Figs. 7-12 an iron frame 68 carries at each side a number of horizontal bars 6| of metal or other material, which form the supports for a number of thin strips or plates 62 of insulating material. Each plate 62 rests on two pegs 63 fixed one at each end of the bar 6! and fitting in slots 64 at the bottom edge of the plate 62.

The insulating plates 62, of which there is one for each selector, are provided with rectangular holes 65 (in number equal to the number of conductors in the bank) through which projecting lugs 66, 61, 68 of the metal strips 69, 1|], H are slipped, forming three rows of multiple contacts corresponding to the contact springs a, b, c of the brushes C of the selectors. Thus the active contact surface of said lug consists of the edge at the extreme end of it, as will be best seen from Figs. 2 and 3.

The upper half of the multiple bank is arranged for the line finders, which require a special test terminal e (also visible in Fig. 2) for finding the group of lines in which a call occurs, while the lower half of the multiple is intended for the final selectors or connectors.

It will be understood that the metal strips 69, 10, H are supported only by means of their contact lugs 66, 61, 68, projecting through the insulating plates 62 in exactly the same manner at both sides of the multiple bank. Thus there are no screws or any other components required for fixing the metal strips which are precisely located at proper distances from each other by the punched holes in the insulating plates 62.

The metal strips 69, 10, II have differently shaped contact lugs as will be seen from the Figs. 14-17, the lugs 61 of the middle strip (the so-called b-conductor) being plain, while the lugs 65 and 68 of the outer strips (the aand cconductors) are bent in opposite directions, so that the contact points of all thiee conductors will be located along the same vertical line. The object of this measure is to make it possible to use exactly similar selectors for both sides of the multiple bank. For this purpose it is, however, also necessary to place the selectors at one side (the back side) of the selector rack in a reversed (upside-down) position, as shown in Figs. 2 and 3. A further condition for this arrangement is also that the three rows of multiple contacts, as well as the springs a, b, c of the selector brushes C are located symmetrically in relation to the common centre line of the multiple contacts and the brushes belonging to one selector. It is obvious that the aand csprings of the brushes C of a selector in the upside-down position will have their functions exchanged, the o-spring serving (in place of the aspring) to complete the talking circuit and the a-spring to close the busy test circuit.

This exchange of connections for the upsidedown mounted selectors is, however, done in a fixed jack on the selector rack, by means of which all conductors of the selector itself are automatically connected to their corresponding conductors of the selector rack, and for this reason no alteration whatever is required, if a selector is moved from one side of the rack to the other. The advantage of this arrangement is evidently, that spare selectors may be used for either side of the rack, so that only one kind of spare selectors need be kept in stock in the exchange. A further advantage is of course, that the manufacture of the selectors will be cheapened by the reduction of the number of different kinds of selectors.

It will be observed that the metal strips 59 and H! for the talking circuit extend through the upper as well as through the lower half of the multiple bank, because these conductors are common to the line finders and the connectors, while the metal strips El and 72 for the busy test circuits are provided separately for the line finders and for the connectors. The metal strips 69, Hi and 12 are provided with soldering tabs 13, l4, 5 at their lower end, While the metal strip H for the busy test circuit for the line finders is provided with a soldering tab 16 at its upper end. The contact lugs 78 of the metal strips 12 for the test circuit of the connectors are of exactly the same shape as the lugs 88 of the strips "H for the test circuit of the line finders. All soldering tabs, which of course are provided for the connection with cable leads, are projecting through insulating plates 62, 11 in the same Way as the contact lugs. Thus the top and bottom sections (at one side) of the bank receive no selectors but are only provided for the cable connections.

The inside of the insulating plates 62 should preferably be covered with some elastic medium, for example oiled silk or the like, in order to prevent any vibration or rocking movement of the contact lugs, when the selector brushes slide over them. The above described multiple contact bank has in addition to the above mentioned uniformity of selectors for the front and back side of the bank, also the advantage of giving a great exactness with regard to the location of the contact lugs without the necessity for elaborate processes for adjustment, while it has'a very simple construction and is cheap to manufacture. It has further the advantage, that those parts of the metal strips, which need not be exposed for the cable connections and the selector brushes, are enclosed in a practically dustproof fashion. To complete the enclosure, formed by the insulating plates 62 and H, the openings at the top and bottom of the bank may be closed up by means of two strips 19 and 80, preferably of the same material as the plates 62.

What I claim is:-

1. A double-sided multiple contact bank for automatic telephone selectors, comprising parallel insulating plates, conductors in the form of sheet metal strips arranged between and with their flat sides at right angles to said plates, each strip being provided with a plurality of projecting lugs, which protrude through holes in the insulating plates and outside these plates form the actual multiple contacts for a plurality of selectors, the

brushes of which have a movement transversely to the metal strips.

2. A double-sided multiple contact bank, for automatic telephone selectors, comprising parallel insulating plates, conductors in the form of sheet metal strips arranged between and with their flat sides at right angles to said plates, each metal strip being supported solely by several projecting lugs, which protrude through holes in the insulating plates and outside these plates form the actual multiple contacts for several selectors, 16 the brushes of which have a movement transversely to the metal strips.

3. A double-sided multiple contact bank, for automatic telephone selectors, comprising parallel insulating plates, conductors in the form of 20 sheet metal strips arranged between and with their fiat sides at right angles to said plates, each metal strip being supported solely by several projecting lugs, which protrude through holes in the insulating plates and outside these plates form the actual multiple contacts-for several selectors, the brushes of which have a movement transversely to the metal strips, said insulating plates being supported by bars extending in a direction parallel to the direction of movement of the selector brushes.

4. A double-sided multiple contact bank for automatic telephone selectors, comprising parallel insulating plates, conductors in the form of sheet metal strips arranged between and with their flat sides at right angles to said plates, each strip being provided with a plurality of projecting lugs, which protrude through holes in the insulating plates and outside these plates form the actual multiple contacts for a plurality of selectors, the brushes of which have a movement transversely to the metal strips, an elastic medium covering the inner surfaces of said insulating plates to hold the metal strips tightly and to prevent vibration. 5

5. A double-sided multiple contact bank, for automatic telephone selectors, comprising parallel insulating plates, conductors in the form of sheet metal strips arranged between and with their flat sides at right angles to said plates, each metal strip being supported solely by several projecting lugs, which protrude through holes in the insulating plates and outside these plates form the actual multiple contacts for several selectors, the brushes of which have a movement transversely to the metal strips, an elastic medium covering the inner surfaces of said insulating plates to hold the metal strips tightly and to prevent vibration.

6. A double-sided multiple contact bank for automatic telephone selectors, comprising plates of insulating material arranged parallel to each other and having apertures, sheet metal strips having a plurality of projecting lugs of the same shape and size on opposite sides thereof, said metal strips placed between said insulating plates with their fiat sides at right angles thereto, said lugs protruding through said apertures in' the plates.

7. A double-sided multiple contact bank for automatic telephone selectors, comprising two plates of insulating material arranged parallel to each other and provided with a plurality of apertures, metal strips having a plurality of contact lugs projecting from opposite sides thereof,

said lugs inserted in said apertures and forming the only support for the said metal strips.

8. In automatic telephone systems of the multiple wiper type, including rows of multiple line contacts, a selector having a slide movable forwards and backwards in front of a row of'said multiple line contacts, wipers on said slide, a sliding rod engaging with said wipers when moving in one direction for selection of one of the wipers and setting it in working position, said sliding rod when moving in the opposite direction engaging with said wiper carrying slide for moving the selected wiper to the contacts of an individual line, and an individual electric motor with a revolving armature geared to said wiper selecting rod and adapted to rotate in one direction when receiving impulses for the selection of contact groups and in the opposite direction when receiving impulses for the selection of in dividual lines.

9. In automatic telephone systems of the type having selectors each including two movable switching members, one of which is a member carrying a number of wipers while the other is a wiper selecting member adapted to set the wipers, one at a time, in working position, the combination with each selector of an electric motor geared to said wiper setting member for driving it forwards and backwards, said wiper setting member during its reversed movement engaging with the wiper carrying member by means of a one-way coupling, thereby moving the set wiper to the terminals of a selected line.

16. Automatic telephone systems of the multiple wiper type according to claim 9, wherein each selector includes a one-way motion transmitting device for coupling said wiper carrying member to said wiper selecting member when the latter is driven by the motor in the reversed direction.

11. Automatic telephone systems according to claim 9, wherein said one-way couplings comprise a pawl and ratchet, said pawl being movable to one side or the other from its normal position and adapted to be released from the engagement with the teeth of the ratchet by first sliding to the end of the ratchet and then along the opposite, toothless edge of the ratchet, thereby allowing the wiper selecting member to return to its normal position.

12. Automatic telephone systems according to claim 9, wherein wipers are mounted on pivots on the associated wiper carrying member, the individual contact springs of each wiper being electrically connected with corresponding contact springs of adjacent wipers by means of helical springs.

13. An automatic telephone system of the type including selectors .each having a reciprocating member for setting a wiper in active position in front of a group of multiple line contacts and for moving said wiper to a selected line in the group, and means for actuating the wiper setting member, characterized by the fact that said means comprises an electric synchronous motor for .each selector, the motor being designed according to the two phase alternating current principle, and having its revolving armature geared to said reciprocating wiper setting member and adapted to be driven forwards and backwards, said armature being operable either by an ordinary combination of two alternating currents with approximately 99 difference of phase, or by a combination of direct current impulses having collectively the character of said two phase alternating current combination.

14. A selector for automatic telephone systems according to claim 13, wherein said motor has a plurality of phase windings, one of the phase windings of the motor connected to impulse contacts on a primary impulse relay pulsating in synchronism with a subscribers dial or an equivalent impulse sender, while the other phase winding of the motor is connected to contacts on a secondary impulse relay which with retardation pulsates in synchronism with said primary impulse relay.

15. A selector for automatic telephone systems according to claim 13, wherein said motor has separate windings for two phase currents, and a retarding device is inserted in one of said phase windings, both phase circuits being connected to a single phase alternating current generator.

16. A selector for automatic telephone systems according to claim 13, wherein the motor has a pair of phase windings to receive impulses from the same relay contacts, which are common to the circuits of both phase windings, and means to retard the impulses in one of the phase windings.

17. A selector for automatic telephone systems according to claim 13, wherein said motor has two 5 pairs of field magnets, each of said pairs of field magnets having two windings acting in opposite directions, and means for alternately supplying impulses to the respective windings of each pair from the same pole of a central source of direct 3 current energy, thereby causing the changes of polarity of the field magnet poles.

18. A selector for automatic telephone systems according to claim 13, wherein said motor has two pairs of field magnets, each of said pairs of field magnets having two windings acting in opposite directions, means for alternately supplying impulses to the respective windings of each pair from the same pole of a central source of direct current energy, thereby causing the changes of 40 polarity of the field magnet poles, and an inductance or retardation coil provided with two windings, connected in the two field circuits in such a manner that the choke and transformer effects of said coil jointly produce a retardation of the reversal of poles of one of the pairs of field magnets at every impulse from the source.

19. A selector as claimed in claim 13, in combination with means for locking the selector in the speaking position for purposes of inspection, said means including a door adapted to be opened to permit access to and inspection of the selector, a selector locking circuit for establishing a continuous current flow through the motor windings, and a normally open switch in said circuit and operable to closed circuit position upon the opening of said door.

20. An automatic telephone system having a plurality of selectors each cooperating with rows of multiple line contacts, each of said selectors including a slide movable forwards and backwards adjacent a row of said contacts, wipers on said slides, a sliding rod on each slide and operable when moving in one direction to select one of said wipers to set the same in working position, said rod being operable when moving in the opposite direction to move the associated slide to engage the selected wiper with the contacts of an individual line, and a reversible electric motor individual to each selector for moving the associated sliding rod in one direction for the selection of contact groups and in the opposite direction for the selection of individual lines.

21. An automatic telephone system as claimed in claim 20, wherein the armature of each motor is geared to its associated sliding rod.

22. A double-sided multiple contact bank for automatic telephone selectors, comprising a main plate of insulating material and a plurality of minor plates of insulating material spaced from and parallel to said whole plate, all plates being provided with a plurality of apertures, sheet metal strips between said main plate and said minor 10 plates, said strips being arranged in planes substantially normal to said plates and each having a plurality of contact lugs projecting from opposite sides thereof, and inserted in said apertures.

23. A double-sided multiple contact bank as claimed in claim 22, in which also the said. main plate of insulating material is divided into a plurality of minor plates.

BERTIL JOHAN BRANDER. 

